The present invention relates to temperature compensated surface acoustic wave (SAW) devices.
SAW devices utilize the localized propagation of acoustic waves on the surface of a planar piezoelectric substrate. SAW transduction between electrical signals and acoustic waves is accomplished by thin film metallic interdigital electrodes on the substrate surface. SAW propagation velocity is temperature sensitive, but SAW devices must often work over a wide temperature range, so devices may be mounted in a custom oven to maintain a fixed temperature above the maximum ambient temperature.
An oven comprises a device holder, heater, temperature sensor, feedback temperature controller, thermal insulation, and electrical connections between the device and ambient. An oven contains (and is thus larger than) the ovenized device and consumes significant power.
One example of an attempt to provide more efficient temperature compensation for a SAW device, is described in U.S. Publication 200810055022A1. The SAW substrate is contained within a vacuum housing which in turn is within a packaging, and a heater is located on the housing or the bottom of the SAW substrate, opposite the acoustic propagation surface. Although a distinct oven around the packaging is avoided, the heater is still remote from the propagation surface of the SAW substrate.